160 AN EXPERIMENTAL STUDY OF RADIO-ACTIVE HTBSTANCES. 



became .sensitive, the screen of plutino-lniriuni cyanid was (iistinctly 

 seen to fluoresce feebly. 



The small specimens of these bodies had no perceptible influence in 

 exciting phosphorescence of sulflds of the alkaline earths exposed to 

 the.r action. 



Having- at hand no apparatus for measuring the electrical conduc- 

 tivity of the air, my experiments were chiefly directed to ascertaining 

 the i*'.->ion of the rays on sensitive plates. 



The photographic experiments were made with Seed nonhalation 

 dry plates (No. 2^!). To test the approximate actinic power of the 

 bodies "A" and '*B," sections of sensitive plates at distances of 5 and 

 10 inches were exposed at intervals of from 2 to 12 minutes. These 

 gave bands varying in intensit}' with the duration of action. "B" 

 showed far greater power than "A." B}' exposing sensitive plates 

 behind an ordinary negative to the entire 10 grams of "radium"' from 

 two to three hours, good transparencies were obtained. On substitut- 

 ing Eastman's bromide paper, prints were secured. The distance of 

 the sensitive surfaces from the source of light was about 3 inches. 



To get skiagraphic images, plates were envelojxHl in Carbutt's black 

 paper (nonpermeable to light), and on this was laid a piece of tin foil 

 cut in openwork pattern. After one hour's exposure a negative was 

 obtained plainly showing the pattern. "A" was apparently stronger 

 than "B." 



Analogous experiments were carried out with the specimens of 

 "radium" and of "polonium" from Paris. Making allowance for the 

 ditt'erence in weight, the radium of German origin was about Ave times 

 as acti\e as the French. The sample labeled " i)olonium subnitratir' 

 (weighing 4 grams) had positively no action on the plates used. 



Having at my disposal 500 grams exceedingly well-purifled uranic 

 nitrate (remaining from previous researches), 1 examined it for Bec- 

 querel rays, Init a sensitive plate exposed three hours to the beautifully 

 fluorescent crystallized stilt gave no trace of action. 



Another incidental expeiiment may be here mentioned. Having 

 seen it repeatedly stated that Rontgen rays exist in sunlight, I endeavored 

 to test the assertion. I placed in brilliant rays of sun a sensitized plate 

 (Seed, No. 26) inclosed in an ordinary plate holder, on which was laid a 

 thick sheet lead perforated with half inch holes, in form of a quincunx. 

 After six hours" exposure the plate was developed in the usual way 

 and no image was obtained. The plate holder itself proved to be light 

 tight. 



The primary source of the energy manifested b}^ these extraordinary 

 substances has greatlj" puzzled physicists, and as yet remains a myster3\ 

 ]Madame Curie, speculating on the matter, at first proposed the follow- 

 ing explanation: She conjectured that all space is continually traversed 

 by rays analogous to Rontgen rays, but far more penetrative and not 



